1. Field of the Invention
The present invention relates to a deflection yoke which is mounted on a cathode-ray tube, and more particularly, to a deflection yoke which is capable of suppressing the generation of unnecessary radiant magnetic fields.
2. Description of the Related Art
Conventional deflection yokes have been proposed in the specification of, for example, Japanese Patent Unexamined Publication No. 63-26928. This deflection yoke (the first conventional technique) has a pair of upper and lower loop-shaped cancelling coils for suppressing the generation of unnecessary radiant magnetic fields externally on a core and in the vicinity of a vertical axis. Japanese Patent Unexamined Publication No. 63-76245 discloses a deflection yoke (the second conventional technique) with two pairs of auxiliary coils for suppressing the generation of unnecessary radiant magnetic fields disposed along the sides of the horizontal deflection coil. Part of each of the coils is covered by a conductive shielding member.
In the first conventional technique, when the numbers of turns for the auxiliary coils are selected such that an unnecessary radiant magnetic field is completely cancelled on the side of the deflection yoke which is close to a fluorescent surface (hereinafter referred simply to as "in front of the deflection yoke"), the auxiliary coils generate an unnecessary radiant magnetic field having a polarity opposite to that of the unnecessary radiant magnetic field of the deflection yoke on the side of the deflection yoke which is close to an electron gun (hereinafter referred simply to as "at the back of the deflection yoke"). In the second conventional technique, shielding of the auxiliary coils makes the structure of the deflection yoke complicated. Furthermore, since the size of the auxiliary coils is large, the resultant deflection yoke requires a large space in an image display apparatus which employs it.